Table of contents:
- Mechanisms of aggression
- Mesenteric threads
- Terpenoid compounds
- Coral aggression management
Video: Coral Aggression
Looking at photographs and images of reefs, the first thing we see is the diversity of species and living organisms. The entire space of the reef is occupied by inhabitants, each of which occupies its own niche. This diversity is the result of the evolution of organisms through competition.
One of the factors underlying competition is aggression, both indirect and direct. Aggression occurs in corals as a result of their constant struggle for survival. Corals have to fight the current, predatory fish, invertebrates, other corals, for example, for light, space and nutrients.
Mechanisms of aggression
Over the course of evolution, corals have evolved several mechanisms to fight for survival. Among them are tentacles, mesinterial filaments, and terpenoid compounds. The picture clearly shows the incompatibilities between some coral species. This behavior can be reflected by color changes such as discoloration of a part of the coral. In response to the proximity of other corals, mushroom corals concentrate venom at the whitening ends of their tentacles.
Related article Coral color: pale, chlorophyll and other pigments
Nematocysts are perhaps the most typical and most common form of defense in hard corals. These mouthless, elongated tentacles act as patrols for the colony. When a tentacle collides with another coral, it can literally "burn" and kill it, or severely damage it.
"Burning" is the result of the work of special cells located in nematocysts. The chemical present in them is essentially an alkaline toxin that can be classified as a poison. This explains the meaning of the saying about corals "sting each other". The toxicity of nematocysts varies with the size and type of coral, just as the length of the tentacles themselves can vary.
The degree of toxicity is very important because:
- If two corals attack each other, the toxicity of the nematocysts will indicate how long they can be in contact with each other without serious damage. There were even cases when corals died within 15 minutes after contact with unfriendly neighbors.
- If two corals have approximately the same toxicity, then they can simply kill each other if they collide. This is why every precaution must be taken to ensure that corals do not fall on top of each other.
The length of nematocysts is not related to the length of normal tentacles and in fact they can be many times longer. This can be most clearly seen on the Pavona cactus coral, a coral whose branches are only a millimeter thick and resemble potato chips. Despite the fact that the branches are only a couple of millimeters thick, the nematocysts emerging from them can reach five to six centimeters. Another colorful example of elongated tentacles is the star coral - Galaxea fascicularis. Normal tentacles in this coral are about two centimeters long, while nematocysts can reach thirty and are very toxic. Thus, keeping such a coral requires a fairly large empty space around it.
Nematocysts can appear when a coral is close to other coral species - it senses its aggressive neighbor.
In addition to nematocysts, some hard corals (Favia, Favites, Scolymia, Pavona, Cynarina, etc.) have mesinterial filaments that play an important role in digestion. These filaments are capable of killing or damaging other coral by a simple digestion process.
Structure of eight-pointed and six-pointed corals
Soft corals compete with hard corals by releasing terpenoid compounds into the water to damage or slow the growth of nearby corals, and then outgrow them in a process called allelopathy. As the name says, these compounds are similar to turpentine and in most cases are extremely toxic. By releasing these components into the water, soft coral damages neighboring hard corals - as a result, it grows faster and takes away almost all the light, which leads to the death of the hard coral.
Coral aggression management
Even though the miniature reef does not contain so many life forms, all conditions must be met to keep aggressive behavior of corals to a minimum. This can be achieved by leaving sufficient space for the corals, anchoring them well, and taking action when aggression occurs.
Providing free space. As noted above, the aggressiveness varies among different coral species. Therefore, when setting up an aquarium, there should be a place free from other invertebrates around each coral.
Related article Invertebrates in a marine aquarium
- for LPS corals (large irrigated) - this distance should be at least 15 cm in all directions, since the maximum recorded length of stinging tentacles (nematocysts) is exactly this.
- the distance between SPS corals (small polyp) can be reduced to 5-8 centimeters, this will be quite enough.
It is also necessary to recall the growth of corals, and therefore there must still be additional space above these values. It is optimal to have a blank space equal to about 30% of the colony size in the areas where the corals will be placed to grow. This may seem extreme and the tank will look poor and empty. However, in a properly equipped and installed aquarium, this space will fill up within the first year. If this space is not left, then soon you will have to constantly prune corals so that they do not kill each other.
Soft corals: In general, the space between soft corals should not be as large as they do not burn each other to the same extent as hard corals.
Consider the following when placing soft corals:
- Rapidly growing corals will obscure their fellows, effectively depriving them of light.
- These corals should be placed so that their mucus and terpenoid compounds do not touch their neighbors. Corals will cause a minimum of harm to each other if the current is arranged in such a way that, overcoming the coral colony, it will strive for them downward, where the water will already pass through the filters.
Tipping corals. Tipping - means that the coral can eventually break away from its place and fall onto another coral, as a result, it will be burned or seriously damaged. The affected area becomes infectious and over time the entire colony will die. Rollover becomes a problem for SPS corals, which are usually not attached to anything.
Therefore, when placing these corals in the aquarium, use a waterproof epoxy resin to attach them to the habitat until they root themselves. Plastic clamps can serve as an alternative to epoxy, if you do not want to secure the corals "forever". If the colony falls on other corals, it should be removed as soon as possible, rinsed under the current, removing any traces of nematocysts.
We minimize the harm from aggression. In a miniature reef, the consequences of aggression among corals can be dire, if no action is taken, an entire colony can die. If you notice stinging tentacles or mesinterial filaments, you should immediately remove all invertebrates from this coral.
If tentacles appear, then they should be removed immediately. If they touch another coral, remove them immediately. Otherwise, the toxins contained in the tentacle will kill the entire colony. On the other hand, if the aquarium is properly maintained and well set up, and you have no problem with algae, a new colony can grow back in the damaged area.
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